1. Technical Field
The invention relates to an apparatus and method for producing vortex ring bubbles of a gas in a host liquid. It allows these rings to be continually generated under conditions in which the parameters of their generation can be independently controlled over a wide range. It therefore allows one device to produce, within limits, a range of different rings from slow-moving, large rings, to fast-moving, small rings and various combinations in between.
2. Description of the Prior Art
Some forty years ago it was first reported that it that it is possible to generate toroidal ring-shaped bubbles, or ring bubbles as they were then called, of gas rising in liquids. These are in fact vortex rings in which the gas collects in the ring-shaped core and which is thereby made visible as a circular tube of gas. In recent years it has become appreciated that they are a natural phenomenon and have even been observed to be produced by whales and dolphins evidently simply for amusement. Apparently they do this by rapidly exhaling a short pulse of air which self organizes into the ring. Skilled professional divers have also been known to produce them by carefully exhaling a pulse of air upwards. It is now known that the key to formation of ring bubbles lies in the momentary flow of a gas, i.e. a pulse of gas, through a nozzle into a surrounding liquid medium. This is the natural phenomenon that whales and dolphins have learned to exploit, but not just any pulse of gas will work. Apparently, proper adjustment of the parameters that determine the pulse characteristics is critical if rings are to form, as opposed to just normal chaotic plumes of bubbles. It is well known that for a given nozzle shape, there are two parameters that determine the behavior of this kind of pulsed nozzle flow. One is the pressure of the source that establishes the strength of the pulse. Good flow will arise if this pressure is constant and does not decay while the flow exits the nozzle. The other parameter is the time duration of that pulse. Evidently, if both these parameters are within certain ranges of values rings will form, but outside of those ranges rings will not form. Instead, single bubbles or chaotic turbulent jets of bubbles will be obtained. Additionally, variations of these parameters, within the ranges, can be expected to give rise to different kinds of rings. For example, low source pressures, and long duration pulses will generally give rise to large slow moving rings. Conversely, higher pressures and shorter pulses will give rise to smaller, faster moving rings. Ideally, any apparatus designed to generate these rings should allow the operator to easily change the values and thereby create rings of different shape and velocity.
It has often been argued that these toroidal bubbles are analogous to the familiar smoke rings in air. However, they are much more complex as two distinct fluid phases are involved, namely the liquid medium, and the tubular core of gas. It has been known for over a hundred years that a tube of gas in a liquid should spontaneously collapse and break up through the effect of surface tension instability. That this does not happen for the toroidal tube of the ring bubble can be attributed to the stabilizing influence of the circulation around the tubular core. The centrifugal force of the liquid spinning around the core opposes and balances the collapsing force of the surface tension. For the vortex ring bubble, there is also an upward buoyancy force present but that is balanced by a downward cross-flow force arising from the lateral spread of the spinning core of the ring, analogous to the lateral force on a spinning ball. Thus the ring, once formed, will steadily rise and spread out and thin. However, eventually a point is reached where viscosity dampens the energy of the circulation so that surface tension then dominates leading to breakup of the ring. Despite this, very long lived rings can be created before breakup occurs.
Various U.S. patents document methods of producing vortex rings of different co-mingled fluids. U.S. Pat. No. 3,589,603 by Fohl allows two different fluids to come together in a co-annular nozzle and mix to form a vortex ring. The fluid motions are generated by two moving pistons, but the device does not consider the case of one fluid being a liquid and the other being a gas as would be needed for forming a gas-filled ring bubble. The inventor gives no evidence that the device could produce toroidal ring bubbles. U.S. Pat. No. 5,100,242 by Latto uses a technique in which a moving orifice plate generates a ring vortex that can be used to enhance fluid mixing. The inventor claims it can be used in water to produce aerated rings through seeding of the vortex flow with bubbles, but this is not the same as producing ring bubbles which are single, coherent self-organized structures. These structures require very specialized conditions of pulse flow and pulse duration. One example, U.S. Pat. No. 4,534,914 to Takahashi et al. does provide those conditions and describes a device that uses an accumulator with a diaphragm in one wall that unseats a spring loaded valve when under pressure allowing gas to flow out into a nozzle. The nozzle has a second elastic valve at its exit which is driven open by the pressure it is exposed to following the opening of the spring valve. As the flow exits through the two valves, the pressure in the accumulator falls, both valves close, leaving a gas-filled ring vortex forming at the tip of the second elastic valve. In a second embodiment, they replace the spring-loaded valve with an electrically-driven valve and a pressure sensitive switch on the diaphragm inside the accumulator. This electrically-driven valve allows the gas in the accumulator to flow to, and open the second elastic valve once a predefined pressure is reached. After the flow starts and the pressure in the accumulator begins to fall, the diaphragm moves against the switch to close the electric valve. In a third embodiment, they use a timed pulse to an electrically-actuated valve, but the valve is now placed externally upstream of the accumulator so as to feed gas to the accumulator. Opening the electric valve causes the pressure to start to rise in the accumulator, eventually forcing the second elastic valve open, thereby creating the flow. This flow through the second elastic valve continues even after the electric valve is closed and does not stop until the pressure in the accumulator falls below a certain level so that the second elastic valve will close.
An examination of the devices of Takahashi et al. points out the following operating characteristics:
1. The pressure levels where the valves open and close can not be externally controlled, since these are a consequence of the resilience of the valves and of the valve springs in the first embodiment, or of the diaphragm in the second and third embodiments, as well as the resiliency of the second exit valve.
2. In the first embodiment, a pulsed flow is established, but the duration of the flow is not determined by any external timing pulse, but by the pressure-induced movement of the diaphragm against the resiliency of the spring of the first valve. Likewise, the second embodiment uses an electrically operated valve, but nor is it driven by any external timing pulse. It is also activated and deactivated by the pressure-induced deflection of the diaphragm contacting a mechanical switch. Therefore in both embodiments, the duration of the pulse can not be easily changed without changing the mechanical elements of the device.
3. The third embodiment also uses an electrically operated valve, but the timing of that valve does not directly define the time duration of the pulse flow. Opening the electrically-driven valve merely starts to pressurize the accumulator, and it is that pressure that ultimately unseats the second elastic valve, starting the flow. Further, once started, the electric valve does not, and can not shut off the flow through the second elastic valve since it only controls the flow into the accumulator. Instead, it is the volume of the accumulator, the resiliency of the elastic valve and the source pressure that determine when that valve will close. These can not be easily independently controlled or varied in a single device. Therefore, significant reconfiguration of the apparatus is needed to change the parameters as needed for generating vortex rings of different sizes and circulation.
4. All these embodiments use a second valve at the nozzle exit and this is essential for proper operation of the devices. Indeed, the devices will not operate without that additional second valve.
5. In all three cases, the pressure in the accumulator is not constant but must decay during operation if the devices are to work. Whether or not this kind of pressure profile is essential, or even optimal for the formation of gas-filled rings is not clear.
6. With each of the three embodiments, the operator can not be precisely certain as to the exact time when the ring will start to form once the accumulator is raised in pressure as it depends on how quickly gas is fed into the accumulator and when it unseats the valve.
In another example, in U.S. Pat. No. 5,947,784 to Cullen, a very similar device is described. In one embodiment it uses a small spring loaded annular nozzle at the end of a tube into which an operator blows to unseat the valve momentarily and create the ring. That inventor recommends that an annular nozzle is to be preferred since an annular ring is to be generated. The skill of the operator, who effectively acts as another second valve, is what determines the strength and duration of the pulse that creates the vortex ring.
In a second embodiment, the pulse is created by an electrically driven pump actuated by a timed circuit. This is very similar to the third embodiment of Takahashi et al. As before, the pressure at which the vortex forms is a consequence of the resilience of the valves, and the duration of the pulse is also determined by this pressure and the volume of the tubing feeding the valve. Only by using a host of different valves and different sizes of tubing can different pressures and pulse durations be achieved. Changes to these parameters can not be easily implemented without reconfiguration of the apparatus.
The method described by Whiteis (U.S. Pat. No. 6,488,270) is somewhat different and allows a flowing gas to build up in a contained pocket under a plate that tilts around a pivot in response to the gas buildup. This flows the gas to a nozzle and allows it to momentarily escape into the surrounding liquid. In this device, the gas flows out of the nozzle because it is at a higher pressure than the pressure at the exit port on the top of the plate. This is because there is a hydrostatic pressure difference between the contained gas beneath the plate and the nozzle exit. This pressure is not constant during operation, but changes as the gas flows out of the nozzle. The duration of the flow through the nozzle is determined by this varying pressure as well as by the geometry of the tilt mechanism and the size of the captured gas pocket. In a second variation, the gas is fed to an inverted bell-like container and is released by an operator momentarily depressing a lever that opens a valve at the top of the bell thereby creating a flow out of the container. The duration of the flow is determined by the skill of the operator and can not be independently established. In both embodiments, different apparatus will be needed for generating vortex rings of different properties. In particular, both these apparatus, as well as the other devices that have been described, do not lend themselves to producing intense, fast spinning vortex rings, since their mechanical moving parts will not allow either very high pressures or very fast, short duration pulses to be easily established.
Of the various inventions described, only those of Takahashi et al. (U.S. Pat. No. 4,534,914), Cullen (U.S. Pat. No. 5,947,784) and Whiteis (U.S. Pat. No. 6,488,270) do enable the unique conditions of flow to be established such that gas-filled, ring bubbles can form. They all make use of specially configured valves, or the creation of a momentary gas flow, in an attempt to establish the favorable conditions of pressure and pulse duration that are necessary to give rise to gas-filled vortex rings. However, from the preceding discussion, a number of limitations or shortcomings can be identified and which can be summarized as:
1. The various configurations generally require the valve to be at the nozzle exit, or even require the complication of an additional second valve right at the nozzle exit.
2. None of these devices allows easy, independent and direct control of the source pressure. Significant changes to the configuration of the devices are needed to change the operating pressure. Also, some of these inventions even require a falling pressure so as to operate. Actually, it is not clear what is the best or simplest pressure variation during the pulse that will ensure producing ring bubbles as opposed to trails of random bubbles. Indeed, without experimentation, it is by no means obvious that other concepts will even be able to produce the right pressure conditions that favor the formation of organized bubble rings.
3. None of these devices allows easy, independent and direct control of the pulse duration. In the configurations that have been described, this can also only be changed by making significant changes to the configuration of the devices. They do not allow the conditions of operation to be easily xe2x80x9cdialed inxe2x80x9d by the operator.
4. The available range of operation for the devices is limited and they essentially operate at only one condition of pressure and pulse duration for a given geometry. In that sense they can be thought of as xe2x80x9cpoint designsxe2x80x9d with limited operational range. For example, the devices do not lend themselves easily to the generation of small rings which require very short pulse durations and higher source pressures.
5. Further, none of the devices allow the precise time of initiation of the pulse to be defined, but only the start of a sequence of events that may ultimately lead to a pulse and subsequent ring formation. This can be important if there is a desire to have the ring form at a very specific time, as might be the case in scientific applications, or if there is a desire to photograph or film the evolution of the ring, or if it desired to produce controlled sequences of these rings, all of which might require timing the pulse to within a small fraction of a second.
It is therefore the object of the invention to provide a simple and direct means of creating the right conditions of pressure and pulse duration of source flow that will give rise to ring bubbles of a gas in a liquid medium while minimizing the number of mechanical valves etc.
It is another object of the invention to provide a means for generating these rings under conditions in which the pressure of the source flow may be directly, precisely, independently and repeatedly controlled with ease.
It is another object of the invention to provide a means for generating these rings under conditions in which the duration of the pulse of the source flow may be directly, precisely, independently and repeatedly controlled with ease.
It is yet another object of the invention that these rings can be created under a wide range of conditions, so that thin rings of fast rotation and fast translation or thick rings of slow rotation and slow translation can be established with the same apparatus.
It is yet another object of the invention to allow these rings to be created at precisely predetermined times so that they may be created sequentially with the frequency of generation being independently determined and controlled.
To achieve these objectives, an apparatus is described in which an accumulator volume is pressurized with a regulated supply of gas under pressure. This confined gas is connected via a tube to the inlet of an electrically operated solenoid valve that can be opened or closed with a standard electrical timing circuit. The outgoing flow from this valve is directed through a nozzle that protrudes into a tank of liquid.
In operation, the electronic circuitry creates an electrical pulse that momentarily opens the solenoid valve, allowing the gas to flow momentarily from the accumulator into the nozzle. If the gas pressure is within a certain range, and if the electrical pulse is of an appropriate duration, a gas-filled vortex ring, or ring bubble will form and be buoyantly carried upwards away from the nozzle.
To eliminate the need for extra valves, a novel geometry is presented that best allows this to take place and is one that exploits the surface tension or capillary properties of the host liquid and will depend on the exit area that is desired. Various configurations are described that achieve this and include circular nozzle exits for small nozzles, or flattened nozzle exits or exits covered with fine wire meshes for larger nozzle exits.
Other features and embodiments of the invention will become apparent from the following drawings and descriptions that are provided.